Mayor Bloomberg is headed to Al bany today — and if he knows what’s good for him, he’ll be pack ing heavy iron.

Because his enemies will certainly have him in their crosshairs.

Metaphorically speaking, of course.

Yes, it’s that time of year again when the Legislature starts to hold public hearings on the governor’s budget — that is, when the special interests line up to issue instructions to their hirelings.

Those with legitimate interests before the body — like Bloomberg — are lucky to get a lick in.

The mayor will make known his views on Gov. Cuomo’s spending plan — even as he puts the final touches on his own preliminary budget for the city, due later this month.

Of course, this year money’s, uh, just a bit tight; the battle for bucks, already under way, is sure to intensify.

As Cuomo notes, New York’s economy simply can’t be expected to grow at a pace sufficient to sustain the surreal spending hikes — 12 percent, overall — that Albany planned.

But Bloomberg has a sound case to make. The city’s needs are legitimate; he’s done a generally creditable job of keeping his own books in order, and he has a full range of cost-cutting reforms to propose that deserve the Legislature’s respectful attention.

That’s where the trouble will start — for, Cuomo aside, Albany has no institutional interest in efficient, economical government.

Bloomberg will be asking lawmakers to untie his hands, so he can further reduce

city spending without unnecessary further impact on city services while absorbing Albany’s cuts.

Tops on the mayor’s wish list, as we’ve been saying, should be relief from the state law that requires teacher layoffs based on seniority, rather than merit.

With budget cuts set to trigger thousands of pink slips, the so-called Last-In, First-Out rule could absolutely devastate the quality of the city’s teaching staff.

Bloomberg will also press for other vital reforms — changes, for example, in the public-sector pension system, whose costs are growing astronomically.

But the lawmakers who’ll be listening to him by and large answer to the public-sector unions and other special-interest groups that benefit from the status quo.

And they’ll be present in force today, whether physically — or just in spirit.

At the Capitol last week, for example, an alleged “coalition” of special-interest fronts called GrowingTogetherNY all but declared war on Cuomo’s plan, even as it claimed to want to avoid being “confrontational.”

Member groups called his trims to schools “horrendous,” said he got his numbers wrong and demanded yet more tax hikes.

And count on this: They’ll be no more accepting of Bloomberg’s proposals than they are of Cuomo’s.

Indeed, probably less so, because the mayor’s agenda is a dagger at the heart of the institutions that feed the fat cats and their law-making patsies.

The governor is headed in that direction, but he’s not quite there yet.